Proposed Syntax

$_internalSchemaMinItems will be a new MatchExpression. It accepts a nonnegative integer <size> and matches an array whose length is at least that number:

{ <field>: { $_internalSchemaMinItems: <size> } }

$_internalSchemaMaxItems is similar, but matches arrays whose length is no larger than <size>.

{ <field>: { $_internalSchemaMaxItems: <size> } }

This will allow us to implement the JSON Schema "minItems" and "maxItems" keywords.